Does nirsevimab prevent lower respiratory infections caused by respiratory syncytial virus?

QUESTIONIn healthy late preterm and term infants, does a single injection of the novel monoclonal antibody nirsevimab, compared to placebo, decrease the incidence of medically-attended lower respiratory tract infections (LRTIs) caused by respiratory syncytial virus (RSV) in the first 150 days after injection? METHODS DesignThis is a multicenter phase 3 randomized controlled trial. AllocationParticipants were randomly assigned to receive nirsevimab or placebo in a 2:1 allocation.Randomization was stratified by age (<3, 3-6, or >6 months) and by hemisphere (northern vs southern). BlindingInvestigators, parents, and guardians were blinded to the study group assignments. Follow-up periodThe incidence of medically-attended RSV-associated LRTI was followed through day 511 following the administration of the study drug or placebo. SettingThe study enrolled participants in the northern hemisphere in 2019 (150 sites in 20 countries) and the southern hemisphere in 2020 (10 sites in 1 country).Patient enrollment, particularly in the southern hemisphere, was adversely and unexpectedly affected by the COVID-19 pandemic.